The invention relates generally to battery cooling systems and more particularly to an apparatus and method for filling and draining battery cooling systems for electric vehicles.
High-energy batteries are desirable in some applications, such as in electric and hybrid vehicles, because of their superior energy capabilities. For example, sodium-sulfur (NaS) batteries are known which provide 2.5 to 4 times the specific energy of common lead-acid batteries, and 2 to 3 times the specific energy of nickel-cadmium (NICAD) batteries. The normal operating temperatures of such batteries, however, often range from 295 to 340 degrees celsius.
When current is drawn from such batteries, internal waste heat is generated. To control upper end temperatures, some high-energy batteries have cooling systems which circulate a cooling fluid through a heat exchanger internal to the battery to draw excess heat away from the battery.
Several liquid coolants have been employed in battery cooling systems. Dibenzyltoluene (known by the trade name MARLOTHERM S.RTM.) is one such coolant which is particularly suited because of its ability to perform over a wide temperature range. However, a problem associated with hydrocarbon coolants, such as dibenzyltoluene, is that such coolants readily decompose in the presence of oxygen; a reaction which is accelerated at higher temperatures. Such decomposition within the battery cooling system may reduce the rate at which excess heat can be transferred away from the battery.
A problem therefore exists in the servicing of these battery cooling systems because it has heretofore been unknown how to drain and fill coolant from such battery cooling systems without resulting oxygen contamination.